1. Field of the Invention
The present invention relates to a bearing structure for a stepping motor for use in optical disc reproducing apparatuses and magnetic disc recording/reproducing apparatuses.
2. Description of the Related Art
A head transport mechanism which has been conventionally adopted in optical disc reproducing apparatuses and magnetic disc recording/reproducing apparatuses, etc. contains a carriage to which is mounted a head member, such as an optical lens and a magnetic head, and on which is provided an engaging projection, slidably engaged with a helical slot in a screw shaft, by which the carriage is linearly reciprocated by rotating the screw shaft.
According to the conventional head transport mechanism of this type, as shown in FIG. 6, one side 4c of a carriage 4 (for example, an optical pickup) having a head member 4a (for example, an optical lens) is slidably supported by a guide shaft 5, and a pair of loose insertion sections 4d are provided on the other side 4b of the carriage 4. In addition, a mount (not shown), which is a molded article integrated with the loose insertion sections 4d, is projected from the carriage, and an engaging projection (not shown) located between the loose insertion sections 4d and pressed into helical slot 1c of the screw shaft 1b is formed at a distal end of a plate spring member (not shown) which is made of a thin metal plate and fixed on the mount by screws. The engaging projection is pressed into the helical slot 1c so that it comes into linear-contact with the inner wall surface of the helical slot 1c so as to be slidably engaged with the helical slot 1c.
When the screw shaft 1b is rotated in forward and reverse directions by a stepping motor 1, the carriage 4 is linearly reciprocated in the axial direction of the screw shaft 1b.
For this reason, the carriage 4 can be transported in consistent directions through the loose insertion sections 4d.
In addition, in a conventional bearing structure for a stepping motor, as shown in FIG. 7, the distal end of the screw shaft 1b integrated with the motor shaft 1a of the stepping motor 1 is in abutment with a bearing member 2', such as a pivot bearing, having substantially a U-shaped cross section through a steel ball 3, and the screw shaft 1b is pressed in its axial direction by a thrust spring (not shown) of the stepping motor 1.
FIG. 8 is a perspective view showing a conventional bearing member adhered to a chassis. Referring to FIG. 8, the substantially square-shaped bearing member 2' formed of a molding material such as polyacetal has a first circular recess 2a' formed in substantially the center thereof, and a second circular recess 2b' formed inside the first recess 2a'. The steel ball 3 is placed in the second recess 2b'. The bearing member 2' is adhered to a pickup chassis 6' formed of the molding material by outsert molding and screws (not shown), etc.
The screw shaft 1b integrated with the stepping motor 1 is in abutment with the bearing member 2' thus adhered to the pickup chassis 6' through the steel ball 3.
However, according to the conventional bearing structure for the stepping motor, in which the distal end 1d of the screw shaft 1b is in abutment with the bearing member 2' such as the pivot bearing through the steel ball 3, the component of the steel ball 3 is required, so that the number of components increases and the structure becomes expensive. In addition, a step of incorporating the steel ball 3 into the recess 2b' of the bearing 2' is necessary, so that assembly becomes more difficult.
In addition, the adhesion of the bearing member 2' to the pickup chassis 6' by outsert molding or screws encounters problems of a cost increase due to the making of an outsert molding die, an increase in the number of components due to screws, and an increase in the number of steps due to a screwing operation.
Further, when the bearing member 2' is adhered to the pickup chassis 6', and a shock is applied during assembly or transporting such that the pickup chassis 6' is slightly deformed, the mounting position of the bearing member 2' may be slightly shifted due to the deformation of the pickup chassis 6'. The shift of the bearing member 2' causes, for example, deviation from the axis of the screw shaft 1b, and a strong abutment of the screw shaft 1b with the bearing member 2', thereby hindering the rotation of the screw shaft 1b.